I would like to know if we can really trust antiviruses because virus makers check their virus with antiviruses before releasing them. So how can we place our confidence in antiviruses?
Because we know that the antivirus can detect what it was tested to detect.
There is no "silver bullet" in security. There is no one thing that will magically protect everyone from everything in the future. Security is about reducing risks and defending against specific threats.
And eventually, the antivirus makers will be able to detect the new virus. So, really, all you are worried about is the window of time where the new virus is released and when the antivirus starts to detect it. And since no virus can hit all computers at once when it is first released, you also get a reduction in risk by the fact that the chances are low that you will ever see a truly new and novel virus that your antivirus will not detect.